1. Field of the Invention
The invention relates to the field of freewheels and more particularly to the field of disengageable pulleys equipped with freewheels used, for example, to drive alternators in a motor vehicle.
2. Description of the Relevant Art
Disengageable pulleys are being increasingly used to overcome the detrimental effects of acyclic running or sudden engine accelerations or decelerations which occur in combustion engines, in particular at low engine speeds and especially in diesel engines.
In these conditions, the drive belt, which is connected to the engine by the crankshaft pulley, decelerates sharply while the driven pulley, the alternator pulley for example, has a tendency, as a result of inertia, to continue to turn at the same speed. If there is a rigid coupling between the pulley and alternator shaft, the belt is subjected to very considerable stresses during these instantaneous speed variations, with detrimental effects such as abnormal belt fatigue and the associated risks of breakage, slipping of the belt on the pulley, or else vibration of the belt strands between the pulleys. Attempts have thus been made to attenuate these phenomena by incorporating between the driven pulley and the driven shaft a freewheel which allows the pulley to be temporarily uncoupled from the shaft if the pulley suddenly decelerates.
Document JP 11-247 972 discloses a disengageable pulley with a freewheel arranged between two rows of balls. The inner races of the bearing and of the freewheel, along with the shaft on which these parts are mounted, are separate components and hence relatively costly to manufacture separately, to manage and to assemble. The freewheel is of the roller type and requires that lock-up ramps or faces are machined and that each roller is combined with an individual bearing spring, a situation which proves to be relatively costly.
Document JP 09-229 097 describes a disengageable pulley comprising a row of balls and a roller-type freewheel with an inner race mounted on a shaft between a nut and a spacer.
Document JP 09-292 006 discloses a disengageable pulley with a row of balls and a row of cams. The inner race is mounted on a sleeve, itself mounted on the shaft, thus increasing the number of parts and reducing the radial gap available between the races, a situation which may lead to using balls and cams of smaller dimensions but in larger numbers to obtain an equivalent load capacity for the balls and an equivalent torque transfer capacity for the cams. This results in increased manufacturing costs.